And Zacharias said unto the angel, Whereby shall I know this? for I am an old man, and my wife well stricken in years. And the angel answering said unto him, I am Gabriel, that stand in the presence of God; and am sent to speak unto thee, and to shew thee these glad tidings. And, behold, thou shalt be dumb, and not able to speak, until the day that these things shall be performed, because thou believest not my words, which shall be fulfilled in their season.

(Luke, 1 vs 18 – 20)

And so Zacharias was made dumb, for a while. Luke has an appreciation for silence; “But Mary kept all these things, and pondered them in her heart”. Perhaps, over time, Zacharias also came to appreciate silence. His muteness came to seem, not a divine punishment but a sign of esoteric knowledge. Perhaps Gabriel could have said “I shall prove this truth: you will not be able to speak of it.” Silence here is the seal and just as, before drinking, one may check the bottle is well-sealed, so with real knowledge – you will be prevented from speaking of it; first you drink, then the bottle is sealed; and by the seal you know the vintage.